I'm sure that a sustainable model -- in terms of at least a tiny portion of authors, editors, translators, etc. being able to make a living writing -- is impossible without scarcity.

I disagree. Let's take a look at music -- not exactly the same, but an industry that has most of its growing pains behind it, presumably. Is music artificially scarce? No, it's plentiful. I can buy a track for a buck, or use any of the growing number of legal listening services, financed either via a lowish monthly fee of some kind, or some commercials. Never ever am I told "sorry, only 100 people may listen to this song concurrently": I listen to a song, and performing artists get a few cents. Everybody wins.

The same is true for videos. Take Netflix: for a fee, you can rent a given number of DVDs at a time. While there are necessarily constraints for physical items (they only have a certain number of DVDs), no such restrictions exist for streaming video.

Music and video have made the step from physical item to online service. The ebook needs to do the same, and trying to mirror built-in limitations of physical items is, I repeat myself, stupid, desperate and shows a deep-rooted fear of losing a once profitable, but no longer sustainable business model. It's also an uphill battle (or fighting retreat, depending on your point of view); those who refuse to adapt will simply become irrelevant in due course.